A lamp of the type of the preamble of Patent claim 1 has been disclosed, for example, in patent EP 0 172 529. That document describes an electric incandescent lamp, in particular a lamp for a motor vehicle headlight, with a lamp bulb pinched on one side and a lamp base consisting of metal and plastic parts. The pinch base of the lamp bulb is mounted in a metallic holder part of the lamp base, whereas the electric connections of the lamp are configured as contact lugs and are housed in the lower part of the base which is made of plastic. The lower part of the base manifests a cavity into which extend the lead wires of the lamp coming from the pinch base. These lead wires are each welded to an end of a contact lug inside the cavity of the lower part of the base. A potting compound is poured into the cavity to seal off the base. This seal ensures that no moisture, which would cause corrosion of the reflector, enters the headlight through the lamp base.
It is the object of this invention to make available an electric lamp with a gas-tight base which manifests improved construction and, in particular, requires no cement or potting compound for the seal.
The electric lamp in accordance with the invention incorporates a lamp base with a connection region made of electrically insulating material in which the electrical connections of the lamp are housed. The connection region manifests a cavity into which project one or more lead wires coming from the lamp bulb. There they are each connected in electrically conducting manner to the end of an electrical connection configured as a contact lug. The lamp base is sealed off according to the invention by means of one or more shaped parts provided with passages for the lead wires and made of heat-resistant, elastic and slightly compressible material. The shaped part(s) sits on at least one contact lug and abuts with a press-fit both the wall that delimits the cavity and the lead wire(s) lead through. The press-fit is advantageously produced by the at least one contact lug which exerts a pressure on the shaped part(s). In addition the shaped part(s) is (are) advantageously located in precisely matching recesses. The pressure exerted by the at least one contact lug on the shaped part(s) is thus evenly distributed across the entire body of the shaped part(s), and an optimum press-fit of the shaped part(s) is achieved on the adjacent cavity walls and the lead wire(s) lead through. In the preferred embodiment the shaped part(s) advantageously consist of silicon. The use of several comparatively thick-walled, tube-like, silicon shaped part(s) which each have a passage for one of the lead wires projecting into the cavity of the connection region has proven successful.
The ends of the contact lugs extending into the cavity advantageously have a claw-like shape and either hook or claw the cavity wall. A secure provisional mounting of the contact lugs which are under mechanical tension can thus be assured before the welding of the contact lugs to the lead wires. To facilitate the welding of the lead wires to the associated contact lugs, the contact lugs are advantageously each provided with a passage for the lead wire.
The passages for the contact lug(s) in the connection region of the base are each preferably provided with an insert bevel which permits an inclined introduction of the contact lugs relative to the base axis and then tipping of the contact lugs in the base axis.
The cavity of the connection region is closed with a cover which advantageously incorporates a web extending into the cavity which sits on the surface of the contact lug(s) facing away from the shaped part or parts. This web provides additional support for the contact lugs. The connection region of the base preferably consists of heat-resistant plastic.